Ridge segmentation, faulting and crustal thickness in the Atlantic Ocean

Shaw, Peter R.

doi:10.1038/358490a0

Cited by 118 publications

(113 citation statements)

References 20 publications

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“…The general seismicity is confined in the 10-20 km wide active ridge segments. Although new accreted lithosphere shows remarkable symmetry in age and depth relationship across the ridges [Wiens and Stein, 1983], faulting mechanisms of the rift walls vary along the spreading segments due to focused along-axis melt delivery [Lin et al, 1990;Shaw, 1992;Tolstoy et al, 1993;Barclay et al, 2001] and generates heterogeneous bathymetric features along the ridges.…”

Section: Earthquake Locationsmentioning

confidence: 99%

“…These discontinuities include large narrow transform fault shear zones and smaller nontransform discontinuities along the ridge crests. Seafloor topography is controlled by lithospheric age, cooling and random reheating, spreading rate and the crustal structures that result from the pattern of upwelling and melt migration [Lin et al, 1990;Macdonald et al, 1991;Shaw, 1992]. The crust along the ridges is under extension and the ridge-axis discontinuities under shear.…”

Section: Introductionmentioning

confidence: 99%

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Locations of mid‐oceanic earthquakes constrained by seafloor bathymetry

2002

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[1] Earthquakes associated with the creation of new oceanic crust are difficult to locate precisely because they normally occur far away from seismic stations. We assume that epicenters of these events can be constrained by seafloor topography and use the Harvard centroid moment tensor (CMT) focal mechanism of an interplate earthquake to relate the event to either a transform fault (a parallel in a coordinate system defined by the pole of rotation between two plates) or a mid-oceanic ridge (a meridian). Using arrival times from the International Seismological Center (ISC) Bulletin, we have relocated about 1500 globally distributed events for the time period 1976-1998. The ISC locations can be as much as 70 km away from appropriate topographic features. Our new locations support that large interplate earthquakes occur on or very close to the primary bathymetric features. For earthquakes with unknown mechanism or magnitude below the CMT threshold or predate the CMT catalog, we use a simultaneous Joint Hypocenter Determination procedure with respect to the already relocated Master Events (JHDME). We invert for earthquakes first for the Romanche Fracture Zone (RFZ) and then for a region extending from 30°N to 30°S. Seismicity agrees well with the main active ridge or transform. However, a small number of events might be related to the secondary bathymetry features. The improved locations for mid-oceanic earthquakes based on bathymetry could help improve our understanding of the oceanic crustal and deep Earth structure, seismic slip and budget constraint along plate boundaries, and dynamics of plate tectonics.

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Section: Earthquake Locationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Locations of mid‐oceanic earthquakes constrained by seafloor bathymetry

2002

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“…Moreover, northeast dipping reflections on Line A cannot be explained as ridgeward-dipping faults. They may be the image of structures striking at high angle to the ridge axis, although structures parallel to the axis and dipping landward could also be [White, 1984] and tectonic denudation by large-scale normal faulting [Karson and Dick, 1983;Mutter and Karson , 1992;Shaw, 1992].…”

Section: Seamounts Areamentioning

confidence: 99%

The crustal structure of the Canary Basin: Accretion processes at slow spreading centers

Ranero¹,

Banda²,

Buhl³

1997

J. Geophys. Res.

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Abstract. Multichannel seismic reflection and gravity data define the structure of Mesozoic ocean crust of the Canary Basin, formed at slow spreading rates. Single and multichannel seismics show a transition from smooth to rough basement topography from Jurassic to Cretaceous crust and a coeval change in crustal structure. Internal reflectivity of the rough basement area comprises upper, upper middle or whole crust cutting discrete dipping reflections. Lower-crustal reflectivity is almost absent and reflections from the crust-mantle transition are short and discontinuous or absent for several kilometers. In contrast, crust in the smooth basement area is characterized by sparse lower crustal events and common reflections from the crust-mantle boundary. The crustal structure of fracture zones in the rough basement area is associated with depressions in the basement top and in most cases with thin crust. In the smooth basement area, fracture zones exhibit neither a clear topographic expression nor crustal thinning. We interpret these characteristics as indicative of an increase in extensional tectonic activity and decrease in magmatic activity at the spreading ridge associated with a general decrease of spreading rate from Jurassic to Cretaceous times. In addition, the crust imaged across the path of the Cape Verde Hot Spot in the Canary Basin exhibits a widespread lower crustal reflectivity, very smooth topography and apparently thick crust. Our data document significant changes in the structure of crust formed at slow spreading rates which we attribute to thermal changes in the lithosphere due either to variations in spreading rate or to the presence of a hot spot beneath the Mesozoic Mid-Atlantic Ridge.

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“…Previous studies have examined the character of faulting from the inner-floor of the rift valley to the crest of the rift mountains (e.g., Macdonald and Luyendyk, 1977;Searle and Laughton, 1977;Shaw, 1992); Chapter 3 quantitatively examines the spatial and temporal record of brittle strain taken up by faults not only within the rift valley but also on the ridge flank. It is the aim of Chapter 3 to further our understanding of the role o{ normal faulting in the formation and segmentation of ridge topography.…”

Section: Introductionmentioning

confidence: 99%

“…Hundreds(> 450) of seamounts have recently been identified on the inner-valley floor of the MAR rift valley between 24° -30°N alone (Smith and Cann, 1990;1992).…”

Section: Introductionmentioning

confidence: 99%

The geological record of oceanic crustal accretion and tectonism at slow-spreading ridges

Jaroslow¹

1996

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Ridge segmentation, faulting and crustal thickness in the Atlantic Ocean

Cited by 118 publications

References 20 publications

Locations of mid‐oceanic earthquakes constrained by seafloor bathymetry

Locations of mid‐oceanic earthquakes constrained by seafloor bathymetry

The crustal structure of the Canary Basin: Accretion processes at slow spreading centers

The geological record of oceanic crustal accretion and tectonism at slow-spreading ridges

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